Method for operating a fuel injection system for an internal combustion engine

ABSTRACT

A method for operating a fuel injection system for an internal combustion engine is provided, in which monitoring is performed as to whether an overlapping occurs between a time interval in which one piezoelectric element for injecting fuel into a cylinder is to be charged or discharged, and a time interval in which a different piezoelectric element for injecting fuel into a different cylinder is to be charged or discharged. The monitoring is performed as to whether, in the context of a lower-priority injection, the charging or discharging occurs within a predefined time interval around the point in time of a charging or discharging of a higher-priority injection, the spacings of time-related charging and/or discharging edges (edge overlaps) being determined during operation of the fuel injection system, and the magnitude of the shift and/or shortening of the lower-priority injections with respect to the higher-priority injections being determined therefrom.

FIELD OF THE INVENTION

The present invention relates to a method for operating a fuel injectionsystem for an internal combustion engine.

BACKGROUND INFORMATION

Published German patent document DE 100 33 343 discloses a fuelinjection system for an internal combustion engine, in particular adiesel engine, that includes an injection control system for monitoringand/or for resolving a conflict upon triggering of the actuatorelements, in particular a conflict management system for superimposedinjection curves of piezoactuators.

With so-called common rail piezoactuators, only one triggering edge canbe executed at a time. For reasons of combustion engineering, however,it is necessary to apply the triggering of complementary banks in such away that injections are superimposed. This is possible, e.g., with thecircuit device known from published German patent document DE 100 33 343for interconnecting piezoelectric elements, when thecharging/discharging edges of the piezoelectric elements exhibit nooverlap. With overlapping edges, provision is made in the context of thefuel injection system disclosed in, e.g., published German patentdocument DE 100 33 343, for the triggering action with low priority(hereinafter called the low-priority triggering action) to be shifted orshortened.

It is an object of the present invention to detect and determine edgeoverlaps, and to determine therefrom the necessary degree of timeshifting or shortening out of the overlap region.

SUMMARY

In accordance with the present invention, the above object is achieved,in a method for operating a fuel injection system of the kind describedinitially, in that the edge overlaps are determined during static anddynamic interrupts of a triggering circuit during operation of theinjection system. This determination is accomplished as a function ofthe rotation speed and crankshaft angle of the internal combustionengine.

In this context, individual edge times are examined in pairs foroverlap. Based on the determined edge overlaps, the necessary degree isdetermined of time shifting or shortening.

FIG. 1 shows a diagram of an interconnection of piezoelectric elements.

FIG. 2A shows one example of charging of a piezoelectric element.

FIG. 2B shows another example of charging of a piezoelectric element.

FIG. 2C shows one example of discharging of a piezoelectric element.

FIG. 2D shows another example of discharging of a piezoelectric element.

FIG. 3 shows a block diagram of triggering IC.

FIG. 4 shows a time sequence of interrupts known in the art.

FIG. 5 is a chart plotting low-priority edges versus high-priorityedges, which chart shows collision regions of edge pairs in terms ofangular region.

FIG. 6 schematically depicts the shifting of a low-priority edge laterin time.

FIG. 7 schematically depicts the shortening of a low-priority triggeringaction.

DETAILED DESCRIPTION

FIG. 1 shows piezoelectric elements 10, 20, 30, 40, 50, 60 as well ascircuit arrangements for triggering the piezoelectric elements. Theletter A designates a region depicted in detail, and B a region notdepicted in detail, the separation of which is indicated by a dashedline c. Region A depicted in detail includes a circuit for charging anddischarging piezoelectric elements 10, 20, 30, 40, 50, and 60. In theexample shown in FIG. 1, piezoelectric elements 10, 20, 30, 40, 50, and60 are actuators in fuel injection valves (in particular, in so-calledcommon rail injectors) of an internal combustion engine. In theembodiment described, six piezoelectric elements 10, 20, 30, 40, 50, and60 are used for independent control of six cylinders within an internalcombustion engine; however, any other number of piezoelectric elementscould be used for any other desired purposes.

Region B not depicted in detail in FIG. 1 includes an injection controlsystem F having a control unit D and a triggering IC E that serves tocontrol the elements inside region A depicted in detail. Variousmeasured values of voltages and currents are conveyed to triggering IC Efrom the entirety of the remaining triggering circuit for thepiezoelectric elements. According to the present invention, control unitD (e.g., computer) and triggering IC E regulate the triggering voltagesand triggering times for the piezoelectric elements. Control computer Dand/or triggering IC E also monitor various voltages and currents of theentire triggering circuit for the piezoelectric elements.

In the description below, the individual elements inside region Adepicted in detail will be introduced first. A general description ofthe operations of charging and discharging piezoelectric elements 10,20, 30, 40, 50, and 60 then follows. Lastly, a detailed description isgiven of how both operations are controlled and monitored by controlcomputer D and triggering IC E.

Piezoelectric elements 10, 20, 30, 40, 50, and 60 are divided into afirst group G1 and a second group G2, each of which encompasses threepiezoelectric elements (i.e. piezoelectric elements 10, 20, and 30 infirst group G1, and piezoelectric elements 40, 50, and 60 in secondgroup G2). Groups G1 and G2 are constituents of circuit parts connectedin parallel. With group selection switches 310, 320, it is possible todefine which of groups G1, G2 of piezoelectric elements 10, 20, and 30or 40, 50, and 60 are respectively discharged by way of a commoncharging and discharging device (group selection switches 310, 320 areof no importance for charging operations, however, as described infurther detail below). Piezoelectric elements 10, 20, and 30 of firstgroup G1 are disposed in one actuator bank, and piezoelectric elements40, 50, and 60 in second group G2 are disposed in a further actuatorbank. The term “actuator bank” designates a block in which two or moreactuator elements, e.g., piezoelectric elements, are immovably placed,e.g., encapsulated.

Group selection switches 310, 320 are disposed between a coil 240 andthe respective groups G1 and G2 (the coil-side terminals thereof), andthe switches are embodied as transistors. Drivers 311, 321, whichconvert the control signals received from triggering IC E into voltagesthat are selectable, as necessary, for closing and opening the switches,are implemented.

Diodes 315 and 325 (referred to as group selection diodes) are providedin parallel with group selection switches 310, 320, respectively. Ifgroup selection switches 310, 320 are embodied as MOSFETs or IGBTs,these group selection diodes 315 and 325 can be constituted, forexample, by the parasitic diodes themselves. During charging operations,group selection switches 310, 320 are bypassed by diodes 315, 325. Thefunctionality of group selection switches 310, 320 is thus reduced tothe selection of a group G1, G2 of piezoelectric elements 10, 20, and 30or 40, 50, and 60 only for the discharging operation.

Within groups G1 and G2, piezoelectric elements 10, 20, and 30, andpiezoelectric elements 40, 50, and 60 are disposed respectively asconstituents of parallel-connected piezo branches 110, 120, and 130(group G1), and parallel-connected piezo branches 140, 150, and 160(group G2). Each piezo branch encompasses a series circuit made up of afirst parallel circuit having a piezoelectric element 10, 20, 30, 40,50, or 60 and a resistor (called a branch resistor) 13, 23, 33, 43, 53,or 63; and a second parallel circuit having a selection switch (called abranch selection switch) embodied as a transistor 11, 21, 31, 41, 51, or61, and a diode (called a branch diode) 12, 22, 32, 42, 52, or 62.

Branch resistors 13, 23, 33, 43, 53, and 63 cause the respectivelycorresponding piezoelectric elements 10, 20, 30, 40, 50, and 60 todischarge continuously during and after a charging operation, since theyrespectively interconnect two terminals of the capacitativepiezoelectric elements 10, 20, 30, 40, 50, and 60. Branch resistors 13,23, 33, 43, 53, 63 are of sufficient size, however, to make thisoperation slow with respect to the controlled charging and dischargingoperations, as described below. The charging of any piezoelectricelement 10, 20, 30, 40, 50, 60 within a relevant time after a chargingoperation is therefore to be regarded as invariable.

The branch selection switch/branch diode pairs in the individual piezobranches 110, 120, 130, 140, 150, 160—i.e. selection switch 11 and diode12 in piezo branch 110, selection switch 21 and diode 22 in piezo branch120, etc.—can be embodied as electronic switches (i.e. transistors)having parasitic diodes, for example MOSFETs or IGBTs (as indicatedabove for the group selection switches/diode pairs 310 and 315, and 320and 325).

With the aid of branch selection switches 11, 21, 31, 41, 51, 61, it ispossible to define which of piezoelectric elements 10, 20, 30, 40, 50,60 are respectively charged by way of a common charging and dischargingdevice; the piezoelectric elements 10, 20, 30, 40, 50, and/or 60 chargedin each case are all those whose branch selection switches 11, 21, 31,41, 51, and/or 61 are closed during the charging operation (describedbelow). Usually only one of the branch selection switches is closed at atime.

Branch diodes 12, 22, 32, 42, 52, and 62 serve to bypass branchselection switches 11, 21, 31, 41, 51, and 61 during dischargingoperations. In the example considered, each individual piezoelectricelement can therefore be selected for charging operations, whereas fordischarging operations, either first group G1 or second group G2 ofpiezoelectric elements 10, 20 and 30, or 40, 50, and 60, or both, mustbe selected.

Returning to piezoelectric elements 10, 20, 30, 40, 50, and 60themselves, branch selection piezo terminals 15, 25, 35, 45, 55, and 65can be connected to ground either using branch selection switches 11,21, 31, 41, 51, and 61, or via the corresponding diodes 12, 22, 32, 42,52, and 62, and in both cases additionally via resistor 300.

The currents flowing between branch selection piezo terminals 15, 25,35, 45, 55, and 65 and ground during the charging and discharging ofpiezoelectric elements 10, 20, 30, 40, 50, and 60 are measured byresistor 300. A knowledge of these currents allows controlled chargingand discharging of piezoelectric elements 10, 20, 30, 40, 50, and 60. Itis possible, e.g., by closing and opening charging switch 220 anddischarging switch 230 as a function of the magnitude of the currents,to adjust the charging current or discharging current to defined averagevalues, and/or to prevent them from exceeding and/or falling belowmaximum and/or minimum values, respectively.

In the example embodiment, the measurement itself additionally requiresa voltage source 621 that supplies a voltage of, for example, 5 VDC, aswell as a voltage divider in the form of two resistors 622 and 623. Thepurpose of this is to protect triggering IC E (which performs themeasurements) from negative voltages, which otherwise might occur atmeasurement point 620 and cannot be handled by triggering IC E. Negativevoltages of this kind are modified by addition, using a positive voltagesupplied by the aforesaid voltage source 621 and the voltage dividerresistors 622 and 623.

The other terminal of the respective piezoelectric element 10, 20, 30,40, 50, or 60, i.e. the respective group selection piezo terminal 14,24, 34, 44, 54, or 64, can be connected to the positive pole of avoltage source via group selection switch 310 or 320 or via groupselection diode 315 or 325, and via a coil 240 and a parallel circuitmade up of a charging switch 220 and a charging diode 221; oralternatively, or additionally, connected to ground via group selectionswitch 310 or 320, or via diode 315 or 325, and via coil 240 and aparallel circuit made up of a discharging switch 230 and a dischargingdiode 231. Charging switch 220 and discharging switch 230 areimplemented, for example, as transistors that are triggered via drivers222 and 232, respectively.

The voltage source encompasses a capacitor 210. Capacitor 210 is chargedby a battery 200 (for example, a motor vehicle battery) and a downstreamDC voltage converter 201. DC voltage converter 201 converts the batteryvoltage (for example, 12 V) into substantially any other desired DCvoltages (for example, 250 V), and charges capacitor 210 to thatvoltage. Control of DC voltage converter 201 is accomplished viatransistor switch 202 and resistor 203, which serves to measure currentspicked off at measurement point 630.

For cross-checking purposes, a further current measurement atmeasurement point 650 is made possible by triggering IC E and byresistors 651, 652, and 653, and, for example, a 5 VDC voltage source654; a voltage measurement at measurement point 640 is additionallypossible by way of triggering IC E and the voltage-dividing resistors641 and 642.

Lastly, a resistor 330 (referred to as the total discharge resistor), aswitch 331 (referred to as the stop switch), and a diode 332 (referredto as the total discharge diode) serve to discharge piezoelectricelements 10, 20, 30, 40, 50, and 60 (if outside the normal operation,they are not discharged by the “normal” discharging operation, asdescribed below). Stop switch 331 may be closed after “normal”discharging operations (cyclical discharging via discharge switch 230),and thereby connects piezoelectric elements 10, 20, 30, 40, 50, and 60through resistors 330 and 300 to ground. Any residual voltages thatmight remain in piezoelectric elements 10, 20, 30, 40, 50, and 60 arethus eliminated. Total discharge diode 332 prevents any occurrence ofnegative voltages at piezoelectric elements 10, 20, 30, 40, 50, and 60,which in some circumstances could be damaged by the negative voltages.

The charging and discharging of all piezoelectric elements 10, 20, 30,40, 50 and 60, or of a specific piezoelectric element 10, 20, 30, 40,50, or 60, is accomplished with the aid of a single charging anddischarging device common to all the groups and their piezoelectricelements. In the example embodiment, the common charging and dischargingdevice encompasses battery 200, DC voltage converter 201, capacitor 210,charging switch 220, discharging switch 230, charging diode 221,discharging diode 231, and coil 240.

The charging and discharging of each piezoelectric element isaccomplished in the same manner, and is explained below with referenceto only first piezoelectric element 10 for sale of simplicity.

The states occurring during the charging and discharging operations areexplained with reference to FIGS. 2A through 2D, of which FIGS. 2A and2B illustrate the charging of piezoelectric element 10, and FIGS. 2C and2D illustrate the discharging of piezoelectric element 10.

Control of the selection of one or more piezoelectric elements 10, 20,30, 40, 50, and 60 to be charged or discharged—the charging operationand discharging operation described below—is accomplished by way oftriggering IC E and control unit D by the opening and closing of one ormore of the aforementioned switches 11, 21, 31, 41, 51, and 61; 310, and320; 220, 230, and 331. The interactions between the elements insideregion A depicted in detail on the one hand, and triggering IC E andcontrol computer D on the other hand, are explained in further detailbelow.

With respect to the charging operation, firstly a piezoelectric element10, 20, 30, 40, 50, or 60 to be charged must be selected. To charge onlyfirst piezoelectric element 10, branch selection switch 11 of firstbranch 110 is closed, while all the other branch selection switches 21,31, 41, 51, and 61 remain open. To charge exclusively any otherpiezoelectric element 20, 30, 40, 50, or 60, or to charge severalelements simultaneously, the appropriate element(s) would be selected byclosing the corresponding branch selection switches 21, 31, 41, 51,and/or 61.

The charging operation itself can then occur, as explained below:

For the example embodiment considered, a positive potential differencebetween capacitor 210 and group selection piezo terminal 14 of firstpiezoelectric element 10 is generally necessary for the chargingoperation. As long as charging switch 220 and discharging switch 230 areopen, however, no charging or discharging of piezoelectric element 10takes place. In this situation, the circuit depicted in FIG. 1 is in asteady state, i.e., piezoelectric element 10 retains its charge statewith substantially no change, and no currents flow.

To charge first piezoelectric element 10, switch 220 is closed.Theoretically, first piezoelectric element 10 could be charged by thataction alone. This would result in large currents, however, which mightdamage the elements in question. The currents occurring at measurementpoint 620 are therefore measured, and switch 220 is opened again as soonas the sensed currents exceed a certain limit value. To achieve adesired charge on first piezoelectric element 10, charging switch 220 istherefore repeatedly closed and opened, while discharging switch 230remains open.

Upon closer examination, the conditions occurring with charging switch220 closed are those depicted in FIG. 2A, i.e., a closed circuit iscreated encompassing a series circuit made up of piezoelectric element10, capacitor 210, and coil 240, and a current iLE(t) flows in thecircuit, as indicated in FIG. 2A by arrows. As a result of this currentflow, positive charges are conveyed to group selection piezo terminal 14of first piezoelectric element 10, and energy is stored in coil 240.

If charging switch 220 is opened shortly (for example, a fewmicroseconds) after closing, the conditions depicted in FIG. 2B result:a closed circuit is created encompassing a series circuit made up ofpiezoelectric element 10, discharging diode 231, and coil 240, and acurrent iLA(t) flows in the circuit, as indicated in FIG. 2B by arrows.As a result of this current flow, energy stored in coil 240 flows intopiezoelectric element 10. Corresponding to the energy delivery topiezoelectric element 10, the voltage occurring in the latter rises, andits external dimensions increase. Once energy has been transferred fromcoil 240 to piezoelectric element 10, the steady state of the circuit(depicted in FIG. 1 and already described) is once again attained.

At this point in time or earlier or later (depending on the desired timeprofile of the charging operation), charging switch 220 is once againclosed and opened again, so that the processes described above occuragain. Because charging switch 220 is closed and then opened again, theenergy stored in piezoelectric element 10 increases (the energy alreadystored in piezoelectric element 10 and the newly delivered energy areadded together), and the voltage occurring at piezoelectric element 10rises, and its external dimensions become correspondingly greater.

If the aforementioned closing and opening of charging switch 220 arerepeated many times, the increase in the voltage occurring atpiezoelectric element 10, and the expansion of piezoelectric element 10,take place stepwise.

When charging switch 220 has been closed and opened a defined number oftimes, and/or when piezoelectric element 10 has achieved the desiredcharge state, charging of the piezoelectric element is terminated byleaving charging switch 220 open.

With regard to the discharging operation, in the example embodiment,piezoelectric elements 10, 20, 30, 40, 50, and 60 are discharged ingroups (G1 and/or G2), as described below:

Firstly, group selection switches 310 and/or 320 of group G1 and/or G2,whose piezoelectric elements are to be discharged, are closed (branchselection switches 11, 21, 31, 41, 51, and 61 have no influence on theselection of piezoelectric elements 10, 20, 30, 40, 50, and 60 for thedischarging operation, since in this case they are bypassed by diodes12, 22, 32, 42, 52, and 62). In order to discharge piezoelectric element10 as a part of first group G1, first group selection switch 310 istherefore closed.

When discharging switch 230 is closed, the conditions depicted in FIG.2C occur: a closed circuit is created encompassing a series circuit madeup of piezoelectric element 10 and coil 240, and a current iEE(t) flowsin the circuit, as indicated in FIG. 2C by arrows. As a result of thiscurrent flow, the energy (or at least a portion thereof) stored in thepiezoelectric element is transferred into coil 240. Corresponding to theenergy transfer from piezoelectric element 10 to coil 240, the voltageoccurring at piezoelectric element 10 drops, and its external dimensionsbecome smaller.

When discharging switch 230 is opened shortly (for example, a fewmicroseconds) after being closed, the conditions depicted in FIG. 2Doccur: a closed circuit is created, encompassing a series circuit madeup of piezoelectric element 10, capacitor 210, charging diode 221, andcoil 240, and a current iEA(t) flows in the circuit, as indicated inFIG. 2D by arrows. As a result of this current flow, energy stored incoil 240 is fed back into capacitor 210. Once the energy transfer fromcoil 240 into capacitor 210 has occurred, the steady state of thecircuit (depicted in FIG. 1 and already described) is once againattained.

At this point in time, or earlier or later (depending on the desiredtime profile of the discharging operation), discharging switch 230 isonce again closed and opened again, so that the processes describedabove occur again. Because discharging switch 230 is closed and thenopened again, the energy stored in piezoelectric element 10 decreasesagain, and the voltage occurring at piezoelectric element 10, and itsexternal dimensions, likewise correspondingly decrease.

If the aforementioned closing and opening of discharging switch 230 arerepeated many times, the decrease in the voltage occurring atpiezoelectric element 10, and the contraction of piezoelectric element10, take place stepwise.

When discharging switch 230 has been closed and opened a defined numberof times and/or when the piezoelectric element has achieved the desiredcharge state, discharging of the piezoelectric element is terminated byleaving discharging switch 230 open.

The interaction of triggering IC E and control computer D with theelements inside region A depicted in detail is accomplished by way ofcontrol signals that are conveyed from triggering IC E, via branchselection control lines 410, 420, 430, 440, 450, and 460, groupselection control lines 510, and 520, stop switch control line 530,charging switch control line 540 and discharging switch control line550, and control line 560, to elements inside region A depicted indetail. On the other hand, sensor signals are acquired at measurementpoints 600, 610, 620, 630, 640, and 650 inside region A depicted indetail, and are conveyed to triggering IC E via sensor lines 700, 710,720, 730, 740, and 750.

In order to select piezoelectric elements 10, 20, 30, 40, 50, and/or 60for the execution of charging or discharging operations of individual ormultiple piezoelectric elements 10, 20, 30, 40, 50, and/or 60 by openingand closing the corresponding switches as described above, voltages areapplied or not applied to the transistor bases by the control lines.With the aid the sensor signals, a determination is made of theresulting voltage of piezoelectric elements 10, 20, and 30, or 40, 50,and 60, on the basis of measurement points 600 and 610, respectively,and of the charging and discharging currents on the basis of measurementpoint 620.

FIG. 3 indicates some of the components contained in triggering IC E: alogic circuit 800, memory 810, digital/analog converter module 820, andcomparator module 830. Also indicated is the fact that the fast parallelbus 840 (used for control signals) is connected to logic circuit 800 oftriggering IC E, whereas the slower serial bus 850 is connected tomemory 810. Logic circuit 800 is connected to memory 810, to comparatormodule 830, and to signal lines 410, 420, 430, 440, 450 and 460; 510 and520; and 530, 540, 550, and 560. Memory 810 is connected to logiccircuit 800 and to digital/analog converter module 820. Digital/analogconverter module 820 is furthermore connected to comparator module 830.In addition, comparator module 830 is connected to sensor lines 700,710, 720, 730, 740, and 750, and, as already mentioned, to logic circuit800.

FIG. 4 schematically shows a time sequence of interrupts for programmingthe beginning of a main injection HE (to be described below in moredetail) and of two preinjections VE1 and VE2, as a function of the topdead center point of the crankshaft. As is evident from FIG. 4, in asix-cylinder engine static interrupts are generated, for example, atapproximately 780 crankshaft and, for example, at approximately 138°crankshaft, and these respectively program the beginning of preinjectionVE2 and of preinjection VE1 located immediately before main injectionHE. The ends of these injections are then programmed on the basis ofdynamic interrupts. It is understood that the above crankshaft anglesare indicated merely by way of example, and the interrupts may also begenerated at different crankshaft angles. Although only the programmingof preinjections has been explained above, the same procedure may beused correspondingly for postinjections as well, however, if they are tobe performed.

Calculation for the detection of edge overlaps is accomplished in eachstatic and dynamic interrupt. Only overlaps between edges that are knownat the time of the interrupt can be calculated.

In each interrupt, the following steps are performed:

1. The current rotation speed n is ascertained; this rotation speed n isused in the entire interrupt (i.e., the rotation speed is “frozen”).

2. With each interrupt, new information about edges becomes known. Toensure that only current information items are compared in pairs, theinformation status is updated. At each interrupt, a flag for newinformation items is therefore set, and a check is made as to whethertriggering operations for which flags are set have already beenexecuted, in which case the relevant flags are deleted.

3. A determination is made of the edge processing times with respect toan arbitrary reference, e.g., with respect to reference time t=0 at acrankshaft angle phi=0°. The known information about beginning angle,time offset, beginning, and duration is utilized, in consideration ofthe current rotation speed, for extrapolation. The general relationshipamong rotation speed n, angle phi, and time t is indicated by equation(1):n=(phi/t)*c  (1),time being measured in microseconds and crankshaft angle phi in °KW, andconstant c being 166,667 (rpm)/(°KW/μs).

4. The individual edge times are examined in pairs for overlap. Forexample, only pairs belonging to different banks are tested, sinceoverlaps within the same bank result from application errors. The safestrategy, however, is nevertheless to test every conceivable edge pair.

5. A priority is allocated to each injection. A specific priority isassigned to each injection on the basis of system parameters andenvironmental parameters. As a result, for each injection pairing adistinction is made between low-priority and high-priority triggeringactions. Steps are taken to ensure that a switchover of prioritiesduring a calculation run does not have negative consequences. Forexample, an overlap detection and actions may be performed in the staticinterrupt in accordance with the current priority constellation, andthen the priorities may be switched over, i.e., modified. In thesubsequent dynamic interrupt of this pairing, control would need tooccur on the basis of a new priority, which would result, in the worstcase, in an action against the triggering of a higher-priority injection(high-priority triggering action). Consistent priority allocation musttherefore be ensured even in the context of this kind of priorityswitchover. This may be provided by allocating a priority set to eachpairing. The size of the buffer for various priority sets must beselected in such a way that the maximum possible number of changes inthe priority sets during the entire execution of a pairing can bestored. After it has been completely processed, the priority set of apairing is replaced with the current set defined by a priority managerof the electronic triggering circuit.

6. In the overlap examination, the spacing in time between therespective beginnings of the two edges is ascertained. Proceeding fromthat spacing, a decision can be made as to whether an overlap exists.Since the edge times are based on the angles for the injections,particular attention must be paid here to 720° KW overruns. Purely inprinciple, a large number of implementation possibilities areconceivable in terms of spacing calculation and evaluation. In theexample embodiment of the method described below, three calculations areperformed.

FIG. 5 depicts the calculations on the basis of angle, the value of alow-priority edge A being plotted on the abscissa, and the value of ahigh-priority edge B plotted on the ordinate. The high-priority edge is“protected” with regions on the earlier (pre) and later (post) sides. Ifa low-priority edge intersects that region, an overlap exists. Theregions are marked in the illustration. Regions outside 720° KW=phimaxare transferred, in accordance with allocation, into the permissibleregions. The results of the calculations using the following equations:$\begin{matrix}{B - A} & (2) \\{B - A - {phi}_{\max}} & (3) \\{B - A + {phi}_{\max}} & (4)\end{matrix}$are marked in the diagram in FIG. 5. Overlaps that are detected by theindividual calculations are characterized in each case by the samecrosshatching. The angle-based correlation is explained in FIG. 5;transformation into the time region is accomplished using equation (1)explained above. An example using A=50° and B=100° yields, with equation(2), the overlap for given values of earlier (pre) and later (post)shifting.

7. The degree of shift or shortening is ascertained as a function of thedegree of overlap. Shifting is performed in the later direction in sucha way that the low-priority beginning edge is placed after the predictedend of the high-priority edge at a distance equal to a time lead. Theduration is retained upon shifting. The point in time of the dynamicinterrupt, which is coupled to the beginning edge at a fixed spacing, isalso shifted. Shortening occurs in such a way that the low-priorityending edge is shifted in the earlier direction. The point in time ofthe beginning edge is retained. The decision as to whether to shift orshorten depends on whether the beginning edge has already been processedat the moment the overlap is detected. If the beginning edge (this beingunderstood as the beginning of execution of the combustion operation)has already been processed, a shift is no longer possible and onlyshortening can occur. The result is that for all overlaps oflow-priority ending edges, only shortening is possible, since the pointin time at which the overlap is detected can lie only in the dynamicinterrupt of the low-priority injection, but the latter is associatedwith execution of the beginning edge.

As an example, a shift is depicted in conjunction with FIG. 6. Theoverlap is detected using equation (2); the resulting overlap magnitudet_(k) is incorporated directly into the degree of overlap. The degree ofshift is expressed by expression (5) below:t_(k)+time lead+“post” protection region  (5).Expression (5) applies even when the overlap was ascertained fromequation (3) or equation (4).

An example of a shortening of the triggering duration is depicted inFIG. 6. The overlap is once again detected using equation (2); theresulting overlap magnitude tk is incorporated directly into the degreeof overlap. The degree of shortening is expressed by expression (6)below:t_(k)−time lead−“pre” protection region  (6).Expression (6) applies even when the overlap was ascertained fromequation (3) or equation (4).

In addition to primary overlaps or collisions, secondary overlaps orcollisions are also possible. Secondary collisions result, for example,when the low-priority beginning edge is shifted later in the staticinterrupt, but collides with the high-priority ending edge. The point intime at which the collision is detected then lies within the dynamicinterrupt of the high-priority triggering action. With this secondarycollision, the low-priority beginning edge must therefore be shiftedfurther in the later direction. The procedure is analogous in the caseof tertiary overlap or collisions. An example embodiment of the methodprovides that after a checking of all pairings that has ended with thedetection of an overlap and associated action, another pass through allpairings is performed until either an abort criterion based on number ofpasses occurs, or an absence of overlaps is identified.

In another embodiment of the method, detection is performed of undesiredoverlappings between the time intervals in which one piezoelectricelement is to be charged or discharged and a time interval in which theother piezoelectric element is to be charged or discharged, bycalculating the utilized angle ranges and comparing them to predefinedpermissible angle ranges, i.e., collision-free or collision-tolerantangle ranges.

A “collision-free angle range” is understood as the angle range that canbe covered by the various injection types of a cylinder of the internalcombustion engine without causing overlaps of triggering actions of theactuators. In the case of a four-cylinder internal combustion enginewith a single-bank structure, for example, the collision-free anglerange is determined by dividing the 720° crankshaft angle value by thenumber of cylinders, i.e., four. In an internal combustion engine ofthis kind, the collision-free angle range is therefore 180° crankshaftangle. The “utilized angle range” is the term for the crankshaft anglerange covered from the beginning of the earliest preinjection to the endof the latest postinjection. If the utilized angle range exceeds thecollision-free angle region then, for example, a late injection for onecylinder overlaps an early injection for another cylinder in the samebank. As already mentioned earlier, only one actuator in a bank can becharged at one time; otherwise a charge equalization would occur thatmight cause disruptions in triggering.

In addition to the single-bank structure, several cylinders can also begrouped into a bank, several banks being triggered by the same supplyunit for charging and discharging. A configuration of this kind iscalled a “quasi-multi-bank” structure. In this case, the angle range inwhich collisions of triggering actions in different banks can beresolved by an edge management system is called the “collision-tolerant”region. In this case, an exceedance beyond the collision-tolerant rangeplus collision-free angle range results in disrupted triggering actions.

Taking the example of a six-cylinder internal combustion engine with aquasi-double-bank structure, the collision-free angle range is 120°crankshaft angle, and the collision-tolerant angle range is likewise120° crankshaft angle. The entire permissible angle range is thendetermined by the sum of the collision-free angle range and thecollision-tolerant angle range; in the case of the six-cylinder internalcombustion engine with a quasi-double-bank structure, the permissibleangle range is 240° crankshaft angle. In general, the permissible angleregion in an internal combustion engine having a quasi-double-bankstructure can be determined by dividing the value of 720° crankshaftangle by the number of cylinders multiplied by the number of banks.

A main feature of the above embodiment of the method for operating afuel injection system for an internal combustion engine is calculationof the utilized angle range and comparison with the permissible anglerange, i.e., the collision-free angle range or the sum of thecollision-free and collision-tolerant angle ranges.

An example embodiment of the method is described below.

In each interrupt, new information items that are used to calculate theutilized angle range become known. In each interrupt, the followingsteps are performed:

1. The current rotation speed n is ascertained; this rotation speed n isused in the entire interrupt (i.e., the rotation speed is “frozen”).

2. With each interrupt, new information about edges becomes known. Thatinformation is converted, using the current rotation speed n, to anangular basis.

3. Each newly arrived angle information item is incorporated into thecalculation of the utilized angle range. From the set of known angleinformation items a minimum/maximum selection is made, with the goal ofascertaining the earliest and latest triggering edge belonging to oneworking cycle. The known utilized angle range is ascertained bydifferentiation from the angle information for the earliest and latesttriggering edges.

After the dynamic interrupt of the last postinjection, the entireutilized angle range from the earliest preinjection to the latestpostinjection is therefore known, the general relationship amongrotation speed n, angle phi, and time t having already been explainedabove in the form of equation (1).

4. The known utilized angle range is compared with the predefinedcollision-free and collision-tolerant angle ranges.

If the ranges are exceeded, an error message is issued and the rangeexceedance is quantified.

5. In all the calculations, consideration is given to rotation speeddynamics with its effect from the time of calculation to the time ofexecution, i.e., triggering of the actuators.

The possibilities for reacting to an error message include:

-   -   a) correspondingly shifting a low-priority injection, so that        the utilized angle range once again lies within the permissible        region; and    -   b) accounting for the error message and the degree of range        exceedance in the context of the next triggering action at the        same or a similar operating point.

1. A method for operating a fuel injection system for an internalcombustion engine having at least one bank of at least two cylinders,the fuel injection system having at least two piezoelectric elements,each cylinder having associated with it at least one respectivepiezoelectric element for injecting fuel into the cylinder by at leastone of charging and discharging the respective piezoelectric element bya supply unit associated with the at least two piezoelectric elements,the method comprising: monitoring for an occurrence of an overlapbetween a first time interval in which a first piezoelectric element isto be one of charged and discharged, and a second time interval in whicha second piezoelectric element is to be one of charged and discharged,wherein the monitoring for the overlap includes monitoring for anoccurrence of at least one of charging and discharging of alower-priority injection within a predefined time interval around apoint in time of at least one of charging and discharging of ahigher-priority injection during operation of the fuel injection system;and determining, based on the overlap, a magnitude of at least one of ashift and a shortening of the lower-priority injection with respect tothe higher-priority injection.
 2. The method as recited in claim 1,wherein injection priorities are predefined, and wherein the predefinedinjection priorities are maintained for one injection cycle.
 3. Themethod as recited in claim 2, wherein a determination of the overlap isachieved during an interrupt of a triggering circuit during operation ofthe fuel injection system.
 4. The method as recited in claim 3, whereina determination of the overlap is achieved based on a rotation speed anda crankshaft angle of the internal combustion engine.
 5. The method asrecited in claim 4, wherein the internal combustion engine has aplurality of banks of cylinders, each bank having at least twocylinders, and wherein the monitoring includes monitoring for an overlapbetween a first time interval in which a first piezoelectric elementassociated with a cylinder of a first bank is to be one of charged anddischarged, and a second time interval in which a second piezoelectricelement associated with a cylinder of a second bank is to be one ofcharged and discharged.
 6. The method as recited in claim 1, wherein adetermination of the overlap is achieved during an interrupt of atriggering circuit during operation of the fuel injection system.
 7. Themethod as recited in claim 6, wherein a determination of the overlap isachieved based on a rotation speed and a crankshaft angle of theinternal combustion engine.
 8. The method as recited in claim 7, whereinthe internal combustion engine has a plurality of banks of cylinders,each bank having at least two cylinders, and wherein the monitoringincludes monitoring for an overlap between a first time interval inwhich a first piezoelectric element associated with a cylinder of afirst bank is to be one of charged and discharged, and a second timeinterval in which a second piezoelectric element associated with acylinder of a second bank is to be one of charged and discharged.
 9. Amethod for operating a fuel injection system for an internal combustionengine having at least one bank of at least two cylinders, the fuelinjection system having at least two piezoelectric elements, eachcylinder having associated with it at least one respective piezoelectricelement for injecting fuel into the cylinder by at least one of chargingand discharging the respective piezoelectric element by a supply unitassociated with the at least two piezoelectric elements, the methodcomprising: monitoring for an occurrence of an overlap between a firsttime interval in which a first piezoelectric element is to be one ofcharged and discharged, and a second time interval in which a secondpiezoelectric element is to be one of charged and discharged, whereinthe monitoring for the overlap includes monitoring for an occurrence ofa crankshaft angle range from the beginning of the earliest injection tothe end of the latest injection that exceeds a predefined permissibleangle range; and determining, based on the overlap, a magnitude of atleast one of a shift and a shortening of a lower-priority injection withrespect to a higher-priority injection.
 10. The method as recited inclaim 9, wherein in an internal combustion engine having a plurality ofcylinders in a single-bank structure, the permissible angle range isdetermined by dividing 720° crankshaft angle by the number of cylinders.11. The method as defined in claim 9, wherein in an internal combustionengine having a plurality of banks each having a plurality of cylinders,the plurality of banks being supplied from a common supply unit in orderto at least one of charge and discharge piezoelectric elementsassociated with the cylinders of the banks, the permissible angle rangeis determined by dividing 720° crankshaft angle by a product of thenumber of cylinders multiplied by the number of banks.
 12. The method asdefined in claim 10, wherein the crankshaft angle range from thebeginning of the earliest injection to the end of the latest injectionis determined by a minimum/maximum selection of angle data for theearliest injection and the latest injection.
 13. The method as definedin claim 11, wherein the crankshaft angle range from the beginning ofthe earliest injection to the end of the latest injection is determinedby a minimum/maximum selection of angle data for the earliest injectionand the latest injection.